Propulsion unit for a water-ski towing device

ABSTRACT

A water-ski towing device including a marine-type motor positioned within a bouyant hull and having a substantially vertical drive shaft extending down through the hull to a propeller drive journaling a propeller at a right angle to the output shaft beneath a cavitation plate. A two-piece shroud comprises an upstream section received in close proximity to the periphery of the propeller and secured to the cavitation plate. A downstream shroud including integral stator vanes is telescoped over and secured to the upstream shroud. The downstream shroud is notched to be received around a tube projecting downward through the anticavitation plate which carries cooling water to the engine. The vanes turn the flow from the tangential to an axial direction to minimize torque reaction on the unit. Additional adjustable trim tabs are provided on selected vanes to tailor the exact amount of turning and flow modification for optimum performance.

United States Patent [191 Uroshevich et al.

[4 1 May 27, 1975 1 1 PROPULSION UNIT FOR A WATER-SKI TOWING DEVICE [76] Inventors: Miroslav Uroshevich, 2505 Fleetwood Ave., Cincinnati, Ohio 45211; Harry V. March, 7223 Gracely Dr., Cincinnati, Ohio 45233 [22] Filed: Oct. 4, 1973 [21] Appl. No.: 403,440

[52] US. Cl 115/6.1; 115/42 [51] Int. Cl B63b 21/56 [58] Field of Search 115/6, 6.1, 12 A, 17, 34 R,

[56] References Cited UNITED STATES PATENTS 899,359 9/1908 Wadagaki 115/42 2,963,000 12/1960 Fester 115/17 2,972,326 2/1961 Simpson 115/6.1 3,310,021 3/1967 Shimanckas 115/17 3,528,382 9/1970 Clark et al. 115/42 Primary ExaminerTrygve Ml. Blix Assistant Examiner-Charles Frankfort Attorney, Agent, or Firm-Irwin P. Garfinkle [57] ABSTRACT A water-ski towing device including a marine-type motor positioned within a bouyant hull and having a substantially vertical drive shaft extending down through the hull to a propeller drive journaling a propeller at a right angle to the output shaft beneath a cavitation plate. A two-piece shroud comprises an upstream section received in close proximity to the periphery of the propeller and secured to the cavitation plate. A downstream shroud including integral stator vanes is telescoped over and secured to the upstream shroud. The downstream shroud is notched to be received around a tube projecting downward through the anticavitation plate which carries cooling water to the engine. The vanes turn the flow from the tangential to an axial direction to minimize torque reaction on the unit. Additional adjustable trim tabs are provided on selected vanes to tailor the exact amount of turning and flow modification for optimum performance.

12 Claims, 5 Drawing Figures PROPULSION UNIT FOR A WATER-SKI TOWING DEVICE It has been proposed in the prior art to provide a water-ski towing device. This type of device comprises a bouyant hull having a motor, a marine propulsion unit and a tow bar extending aft for towing a water skier. Water-ski towing devices require a propulsion unit having horse power high enough to provide sufficient propulsion to pull a skier out of the water to a planing position, but once he is in the planing position the power requirement drastically reduces. It is in this planing condition that many of the prior art devices have experienced problems. These problems are caused by the tangential thrust component of the propeller assembly which causes a reaction roll moment on the bouyant hull. It is particularly aggravated in water-ski towing devices that include an outboard-type motor in which the engine output shaft is vertical and extends to a right angle propeller drive. Examples of this type of unit may be found in the patent to Perkut, U.S. Pat. No. 3,181,493, and Shackner, U.S. Pat. No. 2,914,018. It has been proposed in Moore, U.S. Pat. No. 3,062,172, to enclose an inboard-type motor with a loose fitting shroud and turning vanes to eliminate the torque component. While this type of device is somewhat effective for an inboard type of motor, it does not have the ability to function effectively for an outboard type.

In accordance with one aspect of the present invention the above ends are solved by a marine propulsion device which may be used in the bouyant hull of a water-ski towing device. The propulsion device comprises a motor having an output shaft in a vertical plane. A motor drive housing is positioned at the end of a streamlined strut housing the drive shaft and has an output for rotating the propeller about a horizontal axis. An annular shroud assembly closely surrounds said propeller and has radial vanes combered so as to straighten out the tangential component imparted to the water by the propellers.

The above and other related features of the invention will be apparent from a reading of the following description of the disclosure shown in the accompanying drawings and the novelty thereof pointed out in the appended claims.

In the drawings:

FIG. 1 is a simplified side elevational view of a waterski device having a propulsion unit which embodies the present invention;

FIG. 2 is a greatly enlarged fragmentary longitudinal section view of the propulsion device in FIG. 1;

FIG. 3 is an aft fragmentary view of the propulsion unit of FIG. 2;

FIG. 4 is a greatly enlarged fragmentary view of one of the vanes incorporated with the propulsion unit of FIGS. 1 and 2; and

FIG. 5 is a cross-sectional view of the vanes shown in FIG. 4, taken on line 5-5 of FIG. 4.

Referring to F IG. 1 there is shown a water-ski towing device comprising a lower hull l0 and an upper housing 12 joined at belt line 16. The bouyant hull has a motor 18 positioned in it. Motor 18 receives fuel from tank 20 and provides a vertical rotary output extending downward throughthe hull 10 to a marine propulsion unit 22 to propel the buoyant hull 10 through the wa ter, as described later. An adjustable latch mechanism 24 connects a tow bar 26 to the stem 28 of the hull 10.

Tow bar 26 has a hand grip assembly 30 positioned at its upper end for manipulation by a water skier so that the water-ski towing device pulls the skier through the water and he controls its direction and speed.

FIGS. 2 and 3 particularly show the propulsion unit 22 for this water-ski towing device. Preferably, the engine 18 is a marine-type engine in which the engine has a vertical output shaft directed downward. In this particular instance the normal elongated strut between the motor housing and the propeller drive is eliminated, since the motor 18 is mounted close to the bottom of the hull 10 through an adapter 32 (see FIG. 1). The engine has an airfoil strut housing 34 which extends through a suitably sealed opening in the bottom of the hull 10. Strut housing 34 has an anticavitation plate 36 which is essentially a flange projecting out from the strut 34. A propeller drive housing 38 is supported between the cavitation plate 36 by a propeller support strut 40. The strut 34 also houses a streamlined tube 42 which projects downward through the cavitation plate 36 to connect with the water stream underneath the cavitation plate. Tube 42 has a first passage 44 connected to the water through a screened opening 46 to provide a water cooling supply going up to the engine 18. A second passage 48 carries exhuast gases from the engine and the return cooling water.

An engine drive shaft 50 is connected to the crank shaft (not shown) of the engine 18 and extends downward through suitable couplings to a bevel pinion gear 52 journaled within propeller housing 38. A right-angle drive and clutch assembly comprises a pair of bevel ring gears 54 and 56 interconnected by a sleeve 58 having internal splines. Sleeve 58: is telescoped over external splines on a propeller support shaft 60 journaled within propeller drive housing 38. The set of bevel ring gears 54 and 56 are displaceable along shaft 60 by a suitable mechanism (not shown) to rotate the propeller support shaft 60 in a forward or reverse direction or neutral depending upon the gears 54 and 56 that are engaged with pinion gear 52. The propeller support shaft 60 supports a propeller comprising a conical shaped central hub 62 and suitable propeller blades 64.

What has been described up till now is a usual outboard-type engine in which a vertical output shaft from a motor extends through an airfoil strut and beneath a cavitation plate to a propeller drive housing. It should be noted that thestreamlined tube 42 is included in most outboard-type engines as either functioning as a combined water intake and exhaust or a water intake only.

The above motor is used as an inboard motor by mounting it within hull 10. The apparatus described below is described in connection with the water-ski towing device of FIG. 1, but it may be used in many types of outboard engines secured to the transom of a hull.

To improve the propulsive efficiency of the unit a shroud assembly, generally indicated at 68, is provided around the propeller blades 64. The shroud assembly comprises an upstream inlet ring having a streamlined leading edge shape and an upper flattened section 72 secured to the anticavitation plate 36 by screw as semblies 74 countersunk into the interior surface 76 of the shroud ring 70 to provide a smooth interior flow. The shroud ring 70 has a notch 78 in its downstream edge to clear the streamlined tube 42. The shroud ring 70 also has an aft facing shoulder 80 and an outwardly facing recess 82 at its aft end.

A downstream ring assembly 84 has an airfoil shape and terminates in a trailing edge 86. Downstream ring 84 has a substantial notch 88 for clearing the streamlined tube 42. The ring 84 also has a forwardly facing shoulder 90 connected to an inwardly facing recess 92 spaced from the recess 82. As shown particularly in FIG. 3, the downstream ring 84 is secured to the upstream ring 70 by a series of screws 94 extending through openings 96 in the downstream section radially outward from the recess 82 on the upstream ring 70 and into bosses 98 that are provided at that point to give additional metal to thread into and which form pilot surfaces for the shrouds 70 and 84 relative to one another.

The downstream shroud section 84 has a plurality of radial airfoil vanes 100, 102, 104 and 106. These vanes are preferably cast integral with the shroud ring 84 and extend inwardly to a central conical support section 108 which is coaxial with the propeller blade support 62. The vanes 102-106 are cambered to remove the tangential component of the water accelerated by the propeller blades as they turn through the water.

FIGS. 4 and particularly illustrate the manner in which the blades are cambered. The blade shown in FIGS. 4 and 5 is 106 and has an aerodynamic shape idential to that for the remaining blades so that its characteristics will apply to all. The vane 106 has a root section 1 having a very small stagger angle and a tip section 112 having a greater stagger angle. The leading edge 114 has an incidence angle varying from a maximum at the tip section 112 to a minimum at the root section 1 10. A trailing edge has a substantially constant axially directed exit angle. As is particularly apparent in FIG. 4, the contour of the vanes are defined by straight lined elements extending from the root section 110 to the tip section 112 so that the leading edge pitch is constant. These straight line segments greatly facilitate casting of the shroud ring 84 and vanes as an integral piece.

To further enhance the control characteristics of the unit, as described later, the trailing edges 116 of one or more of the vanes may be provided with trim tabs 118 to enable additional turning of the flow or a modified turning. These tabs are secured as shown herein to the section side 120 of the vane by bolt assemblies 122 extending through axially directed slots 12 in the tab itself. As illustrated, the trim tabs 118 are positioned on vanes 106 and 102. However, they may be positioned on any number of the vanes to further tailor the propulsive flow from the unit. The tabs 118 may either be bent in place or slid into and out of the stream by loosening bolt assemblies 122 to vary their effect on the flow.

To assemble the propulsion unit described above it is necessary to first secure the upstream shroud 70 to the cavitation plate 36 adjacent the propeller blades 64 and then secure the downstream shroud 84 and vane assembly to the upstream shroud 70. The reason for this is that the tight clearances between the tips of the propellers 64 and the inner wall 76 of the upstream shroud 70 make it impossible to do this with a single piece shroud since the shroud must pass and clear the streamlined tube 42 for water and exhaust.

When the device is being operated the propeller blades 64 impart an axial and tangential component to the water passing through the shroud. The shroud makes the propulsive flow extremely efficient but tends to accentuate the tangential component. The vanes 102-106 turn the flow from the tangential to substantially axial direction so that the resultant thrust is substantially in an axial direction. The trim tabs 1 l8 enable the flow to be tailored even more to achieve a precise control over the direction of flow for the particular conditions involved. During start-up condition the motor exerts a rather substantial propulsion thrust in order to minimize the tendency of the hull 10 to lift up in the water. The latching mechanism 24 is positioned extremely low on the hull and the propulsion unit 22 is angled downward with respect to the bottom surface of the hull 10. The angle illustrated is exaggerated but in practice it has been found that approximately one degree downward incidence gives acceptable results. By angling the motor downward and placing the point of connection for the two bar as low as possible on the stem 28, the coupling arm between the propulsion unit and the tow bar is greatly minimized, thus minimizing the tendency of the unit to lift up.

The above unit has been described in connection with a water-ski propulsion towing device. However, it should be apparent that it has particular applicability to improve the propulsive efficiency of any outboard-type engine having the usual geometric constraints in the area beneath the cavitation plate for the unit. The shroud assembly is extremely adaptable retrofit situation because the shroud rings require no modification to the existing equipment other than drilling several holes in the cavitation plate 36 for the screw assemblies 74.

While a particular form of the present invention has been described, it should be apparent to those skilled in the art that it may be practiced in other forms without departing from the spirit and scope thereof.

Having described the invention, what is claimed as novel and desired to be secured by Letters Patent of the United States is:

1. A water-ski towing device comprising:

a bouyant hull;

a motor mounted in said hull and having a vertically oriented output shaft;

a streamlined strut extending downward through said hull, said output shaft extending through said strut;

a propeller drive unit mounted adjacent the lower end of said strut, said propeller drive unit receiving an input from said motor output and having a right angle propeller drive shaft;

a propeller mounted on said propeller drive shaft;

an annular two-piece streamlined shroud secured to said strut and comprised of abutting upstream and downstream annular sections, said annular upstream section of said shroud being positioned around said propeller closely adjacent the tips thereof whereby a propulsive annular stream is directed from said shroud in an axial direction, said annular stream having a tangential velocity component;

said annular downstream section of said shroud supporting a plurality of radial vanes in the flow path of said stream through said shroud, said vanes being angled to turn the flow in a tengential direction opposite to and at least as great in mangitude as the tangential component imparted by said propeller; and an anticavitation plate supported from said strut above said propeller drive unit and wherein said annular shroud is secured to said anticavition plate.

2. A water-ski towing device as in claim 1 wherein said upstream annular section surrounds said propeller and is secured to said anticavitation plate and said annular downstream section is secured to said upstream section.

3. A water-ski towing device as in claim 2 wherein said upstream section has an aft facing shoulder and said downstream section has a forward facing shoulder telescoped over said aft facing shoulder and wherein said device further comprises screws extending through said downstream section and threaded into said upstream section for securing said downstream section to said upstream section.

4. A water-ski towing device as in claim 3 wherein said vanes are radial vanes integral with said downstream section.

5. A water-ski towing device as in claim 4 further comprising trim tabs on the trailing edges of said vanes for varying the degree to which said flow is straightened.

6. A water-ski towing device as in claim 5 wherein said trim tabs have elongated slots and said device further comprises means for adjustably securing said trim tabs to said vanes along said slots for varying the degree to which said tabs act on said stream.

7. A water-ski towing device as in claim 4 further comprising a central conical element coaxial with said propeller and to which said vanes extend.

8. A Water-ski towing device as in claim 7 wherein said vanes are defined by straight line elements extending between hydrofoil cross sections at the tip and root of each vane so that the leading edge pitch is constant.

9. A water-ski towing device as in claim 1 wherein:

said motor includes a cooling water intake projecting downward from said cavitation plate aft of said propeller; and

wherein said upstream section surrounds said propeller and the downstream section is notched to clear said cooling water intake.

10. A water-ski towing device as in claim 9 wherein:

said upstream shroud section is secured to said cavitation plate,

said downstream section is secured to said upstream section, said vanes being formed integral with said downstream section.

1 l. A water-ski towing device as in claim 10 wherein:

said upstream section has an aft facing shoulder at its aft end;

said downstream section has a forward facing shroud at its forward end telescoping over the aft end of said upstream shroud;

said device further comprises screws extending through said downstream section and threaded into said upstream section between said shoulders.

12. A water-ski towing device as in claim 11 wherein said shoulders are spaced to form a gap therebetween and one of said shoulders has spaced pads for precisely positioning the shrouds relative to one another. 

1. A water-ski towing device comprising: a bouyant hull; a motor mounted in said hull and having a vertically oriented output shaft; a streamlined strut extending downward through said hull, said output shaft extending through said strut; a propeller drive unit mounted adjacent the lower end of said strut, said propeller drive unit receiving an input from said motor output and having a right angle propeller drive shaft; a propeller mounted on said propeller drive shaft; an annular two-piece streamlined shroud secured to said strut and comprised of abutting upstream and downstream annular sections, said annular upstream section of said shroud being positioned around said propeller closely adjacent the tips thereof whereby a propulsive annular stream is directed from said shroud in an axial direction, said annular stream having a tangential velocity component; said annular downstream section of said shroud supporting a plurality of radial vanes in the flow path of said stream through said shroud, said vanes being angled to turn the flow in a tengential direction opposite to and at least as great in mangitude as the tangential component imparted by said propeller; and an anticavitation plate supported from said strut above said propeller drive unit and wherein said annular shroud is secured to said anticavition plate.
 2. A water-ski towing device as in claim 1 wherein said upstream annular section surrounds said propeller and is secured to said anticavitation plate and said annular downstream section is secured to said upstream section.
 3. A water-ski towing device as in claim 2 wherein said upstream section has an aft facing shoulder and said downstream section has a forward facing shoulder telescoped over said aft facing shoulder and wherein said device further comprises screws extending through said downstream section and threaded into said upstream section for securing said downstream section to said upstream section.
 4. A water-ski towing device as in claim 3 wherein said vanes are radial vanes integral with said downstream section.
 5. A water-ski towing deVice as in claim 4 further comprising trim tabs on the trailing edges of said vanes for varying the degree to which said flow is straightened.
 6. A water-ski towing device as in claim 5 wherein said trim tabs have elongated slots and said device further comprises means for adjustably securing said trim tabs to said vanes along said slots for varying the degree to which said tabs act on said stream.
 7. A water-ski towing device as in claim 4 further comprising a central conical element coaxial with said propeller and to which said vanes extend.
 8. A water-ski towing device as in claim 7 wherein said vanes are defined by straight line elements extending between hydrofoil cross sections at the tip and root of each vane so that the leading edge pitch is constant.
 9. A water-ski towing device as in claim 1 wherein: said motor includes a cooling water intake projecting downward from said cavitation plate aft of said propeller; and wherein said upstream section surrounds said propeller and the downstream section is notched to clear said cooling water intake.
 10. A water-ski towing device as in claim 9 wherein: said upstream shroud section is secured to said cavitation plate, said downstream section is secured to said upstream section, said vanes being formed integral with said downstream section.
 11. A water-ski towing device as in claim 10 wherein: said upstream section has an aft facing shoulder at its aft end; said downstream section has a forward facing shroud at its forward end telescoping over the aft end of said upstream shroud; said device further comprises screws extending through said downstream section and threaded into said upstream section between said shoulders.
 12. A water-ski towing device as in claim 11 wherein said shoulders are spaced to form a gap therebetween and one of said shoulders has spaced pads for precisely positioning the shrouds relative to one another. 